The present invention relates to a cooking unit, particularly for industrial cookers or the like, with e.g. a glass ceramic hotplate, which is provided on its back surface with at least one radiant heater, which has an insulator with at least one radiant element.
An object of the present invention is to provide a cooking unit of the aforementioned type, which ensures simple assembly in the case of a reliable connection between the radiant heater and the hotplate.
In the case of cooking units of the present type, the glass ceramic plate as such can be fixed to the hob, followed by the fixing of a number of radiant heaters, which constitute separate assemblies, corresponding to the number of cooking points to be provided on the hob. This can easily lead to assembly errors. When using radiant heaters as a heat source, it is particularly important that the insulator firmly engages against the underside of the hotplate, which is brought about by using springs, which are generally positioned or inserted during assembly.
For achieving the objects of the invention, it is also advantageously possible in the case of a cooking unit of the aforementioned type that between the support and the radiant heater is provided at least one spring pressing the same against the hotplate. Unlike in an assembly, where the radiant heater is connected without springs rigidly to the hotplate, this leads to an arrangement in which, within the assembly, the radiant heater is movably mounted with respect to the hotplate at least about a spring displacement at right angles to the hotplate and is pressed against the latter by springs, so that prior to the assembly of the cooking unit in the hob the resiliently pressed engagement of the insulator on the hotplate is obtained and can be checked.
The construction can be significantly simplified in that there are no carrying clips running at right angles over the underside of the radiant heater and instead the support is formed by at least one carrying frame running from the hotplate to the back of the radiant heater and in particular constituted by a bent section and which engages round the back surface of the radiant heater only in the associated border region, so that particularly from the height standpoint the cooking unit takes up little space. The spring can be located between a leg of the support engaging round the back of the radiant heater and the back of said heater, so that it is arranged in a completely sealed and space-saving manner and only requires a very small spring extension in the spring direction making it possible to use relatively rigid springs.
In a particularly advantageous embodiment the back surface of the radiant heater is offset in the vicinity of the support engaging round it, preferably in such a way that the back of the heater is located outside the offset region in a single plane with the engaging round part of the support. Thus, the underside of the cooking unit can be substantially planar over its entire extension, which is particularly advantageous concerning the stackability of the cooking unit, but also facilitates installation.
According to a further development of the invention the spring is supported on a sheet metal or similar cover provided on the insulator which, unlike in the case of a shell-like cover receiving the insulator is preferably formed by an approximately planar base plate leaving the outer circumference of the insulator free, which leads to a further constructional simplification. Appropriately this base plate has the same plan form as the insulator, so that the outer edge surface of the former terminates with the outer circumferential surface of the latter. This cover is advantageously suitable within the outer circumference, particularly in the vicinity of the central cutout, to provide a mounting for a connecting body for the electrical connection of the radiant heater, which can be substantially completely countersunk within the insulator or a central cutout provided therein.
For protecting the outer circumference of the insulator, particularly if it is not surrounded by the cover, it is appropriate for the support to cover the outer circumference of the insulator, especially engaging approximately on the outer circumference, the support appropriately passing in uninterrupted manner over the outer circumference or the outer edge of the insulator.
A high mechanical strength of the closed assembly is obtained if the support forms a frame surrounding the radiant heater.
In an extremely simple manner the support can be connected to the hotplate in that, particularly by means of an outwardly directed leg it is bonded to the hotplate in heat-proof manner, e.g. using a silicone adhesive. The support is appropriately completely located within the outer edges of the hotplate, so that bonding only takes place on the underside of the hotplate.
On the outer circumference of the hotplate it is possible to provide a carrying rim, which is advantageously fixed to the support or to the hotplate or to both these parts by bonding or the like. In the case of bonding with respect to the hotplate, this appropriately takes place with respect to its associated edge surface. It is particularly appropriate if the carrying rim engages below the support, particularly its outwardly directed leg, so that the carrying rim forms a bearing surface for the support and therefore for the hotplate directly over it.
The spring can be constructed in a simple manner as a leaf, corrugated, fastening, cup or similar spring.
According to the invention one hotplate of the cooking unit can be provided on its underside with a corresponding number of separate radiant heaters for forming several separately switch-selectable, adjacent cooking points within a cooking field. The radiant heater is provided with at least one radiant element located in a support shell and which forms a heating field, whilst supported on a substructure it is pressed by springs against the underside of the heating plate.
Electric cookers for cooking large amounts of food, such as are used in industrial kitchens, canteens and the like, generally have as cooking points electric hotplates with hotplate bodies made from cast iron, which are introduced into a hob. Such cookers have proved advantageous from many respects, but there is till a need for easier handling, a lower energy consumption together with more rapidly responding power provision and easier maintenance and repair than is possible with the cooker known from British patent 714,373.
The object of the present invention is therefore to provide a cooking unit of the described type making it possible, in the case of a substantially jointless, liquid-tight construction of the hotplate to provide use regions passing uninterruptedly into one another, which can be heated in such a way that the heating of numerous different heat flow diagrams under one or more cooking utensils placed on the hotplate can be adjusted.
In the case of a cooking unit, particularly of the latter type, the invention solves this problem in that each radiant heater is substantially non-displaceably inserted in a receptacle of the substructure adapted to the external heater dimensions and that the receptacles are approximately directly adjacent to one another, in such a way that the cooking field can be heated substantially without interruption and over at least approximately 85% of its total surface. The cooking field is the field defined by the outer boundaries of an associated group of radiant heaters, so that the hotplate can be larger than this cooking field. Within this cooking field, each radiant heater can be operated independently of the other radiant heaters as a result of its setting or control and its technical data, so that the radiant heaters can be set in such a way that the cooking field is formed by uninterruptedly connected or thermally coalescing heating fields with the same or different power provision and the cooking utensils by movement or displacement can be moved into the desired heating field alone and into zones in which two or more adjacent heating fields act with different proportions as a function of the position of the cooking utensil. Since, with regards to the power provision, cooking units with hotplates and radiant heaters respond much more rapidly than cast metal hotplates, this construction leads to the important advantage that for obtaining a reduced energy requirement, a sensitive setting or control adapted to needs can take place without increasing the cooking times, unlike has hitherto been conventional practice in industrial kitchens the hotplates do not have to be operated at full power over their entire period of use.
For domestic cookers, cooking units with hotplates and radiant heaters are admittedly known, e.g. from DE-OS 22 42 823, which can be brought together to form a relatively large total heating surface, but this has led to the cooking field being made correspondingly smaller, which is disadvantageous due to the reduced heated surface, especially in industrial kitchen cookers. Due to rough use in industrial kitchens, the use of glass ceramic hotplates has been avoided, because such hotplates are relatively sensitive to impacts and breakages. As a result of the almost uninterrupted juxtaposing of the radiant heaters in a non-displaceable position, even in the case of relatively large overall dimensions, the underside of the hotplate is supported by support shells engaging thereon generally with a damping insulating material that there is scarcely any need to fear hotplate breakage even under the most severe conditions.
The aforementioned advantages are particularly obtained if all the radiant heaters are rectangular, particularly square and are connected to one another preferably only with slot-like gaps of a few centimetres, particularly approximately one centimetre. It is particularly advantageous if all the radiant heaters have an identical construction and are e.g. interchangeable, with regards to the rated capacity and the control or setting, to provide different radiant heaters, which appropriately have the same ground plan dimensions, so that e.g. four radiant heaters are provided which form a rectangular or square cooking field. The size of the cooking field is appropriately approximately 300.times.300 mm, e.g. 320.times.320 mm, whilst the edge dimension of the heated surface of the radiant heater is approximately 290.times.290 mm, so that there is a cooking field pitch similar to that of the known industrial cookers.
The receptacles can be formed in a simple manner by angular sections, on whose approximately horizontal legs are independentily supported by means of spring elements the radiant heaters, so that for each heater it is possible to obtain a clearance-free, tight engagement on the underside of the hotplate, in the case of a limited total cooking unit height. Appropriately the hotplate can be removed or raised from the radiant heaters or cooking unit, very simple operation being obtained if the hotplate can be flapped up and on transferring into its operating position by application to upper end faces of outer borders of the support shells of the radiant heaters, the latter press downwards under the pretension of spring elements.
According to a particularly advantageous development of the invention, the radiant heater is operated by means of a temperature regulator or thermostat, so that there is rapid operating readiness, i.e. a heating with maximum power, but nevertheless a low energy consumption in the unloaded state, i.e. in the case where no heat is taken by a cooking utensil, so that a good power adaptation is obtained, which can e.g. be further improved by a continuously adjustable construction of the thermostat. According to another feature of the invention for influencing the thermostat, which is preferably in the form of a capillary tube regulator, between the radiant element and the underside of the hotplate is provided a temperature sensor approximately parallel to the latter and which is preferably rod-like and crosses the associated heating field over most of its associated width. Instead of a system filled with a high temperature expansion fluid it is also possible to provide an electronic or electrical thermostat, whose sensor is temperature-sensitive over its entire length. It has been found that as a result the complete heating field can be substantially uniformly detected and with regards to the overall heat flow of the particular heating field there is a very sensitive and therefore rapidly responding control.
Particularly in the case of a cooking unit of the described type, the invention further provides that a thermostat is associated with the temperature sensor and which is also constructed for temperature limiting purposes, i.e. also ensures that the hotplate does not exceed a predetermined maximum temperature. Thus, there is no need for a separate temperature limiting switch and an associated, separate sensor. In place of the temperature-regulated operation of the particular radiant heater, it is also possible to provide step switching, e.g. a four or seven-cycle circuit by means of a corresponding power control device, if the radiant heater is provided with the corresponding number of separately switch-selectable radiant heaters or heating circuits, which can then be connected in parallel and/or in series for the individual switching stages. However, in this case the hotplate is protected by a temperature limiting device in the form of a thermostat, e.g. a rod temperature regulator with a fixed setting, whose temperature sensor is constituted by a rod having different thermal expansion characteristics positioned in axially abutted manner in an outer tube and which acts on a snap switch arranged in a casing at one end of the temperature sensor. In the case of such step switching, the no-load temperature, i.e. the temperature of the heating field with no power take-off, is given by the fixed setting of the thermostat set to a relatively high temperature. In the case of a rated power of e.g. approximately 4000 W, there is an energy saving particularly if the power control device is set to at least approximately 3/4 of the rated power. The temperature sensor can also be constituted by a tubular sensor similar to a tubular heater, but with temperature-dependent resistance wire, embedded within a metal tube jacket in contact-free manner and therefore in insulated form in an insulating material.
If the radiant heater operation is regulated in temperature-dependent manner, the thermal characteristic of the heating field can be adapted in a surprisingly simple manner to the requirements of industrial kitchens in that the thermostat only switches part, e.g. half the radiant heater power, whilst at least a further or the remaining part of the rated power is switched in by an additional contact of the thermostat in the upper temperature setting range. The thermostat can switch one or more radiant elements, whilst the additional contact switches the one or more other radiant elements. Thus, a low no-load power is obtained for energy saving and hotplate protection purposes and when using the cooking point in a substantially delay-free manner a maximum high power is made available, because the temperature of the cooking point is always held at a set level and if necessary a predetermined power can be switched in. Apart from a rapid operational readiness, the settable control also permits a good power adaptation to the particular conditions, so that the cooking unit can be set to zones of different power or temperature, such as for initial cooking, roasting, further cooking, as well as keeping hot or warming. Instead of this or in addition thereto, the thermostat can also have at least two switching contacts influenced by the temperature sensor and which in each case switch on or off a separate part, i.e. particularly separate radiant elements of the radiant heater at different temperatures. Appropriately each switching contact of the bipolar thermostat switches roughly half the total power of the radiant heater, so that the switching behaviour is similar to that of conventional automatic cast metal hotplates with central sensor, i.e. even in the case of a low thermostat setting initial heating takes place with the full power and is then continued with part of the power. Thus, the radiant heater can only be provided with two radiant elements or heating resistors, which are appropriately positioned parallel to the outsides of the radiant heater and are placed in rectangular or square double spirals in the support shell, in such a way that the radiant heater only has to have four connecting points directly connected to the juxtaposed ends of the radiant elements.
A particularly advantageous further development of the invention is obtained in that at least one radiant element, particularly all such elements of the particular radiant heater can be switched off by means of a cooking utensil identification sensor, which is preferably positioned roughly in the centre of the heating field below the hotplate and is screened by an insulating jacket, so that the temperature sensor is positioned outside the centre of the radiant heater immediately alongside the insulating jacket and parallel to two outsides of the radiant heater. The identification sensor, whose snap switch is appropriately connected in series with the thermostat or power control device, makes it possible to ensure that there is no energy consumption under no-load conditions, despite the switched in radiant heater, whilst on setting down a cooking utensil the full power is immediately available. The identification sensor can e.g. operate optically, but particularly reliable operation is obtained if it is constructed as an inductively operating sensor.
To ensure that the hotplate is tight against food and the like which has run over or spilled, whilst enabling easy cleaning at all times, it is appropriately connected in liquid-tight manner to a frame running round its outer edges, said frame extending at the most up to the plane of the top surface of the hotplate or projects slightly above the same, so that the cooking utensils can always be moved over the border of the cooking unit, without any hard impacts occurring to the hotplate. In certain cases, namely e.g. where, for reequipment purposes, cast metal electric hotplates are to be replaced by radiant heater cooking points, it is also possible to integrate the particular radiant heater with a separate glass ceramic or similar hotplate corresponding roughly to the size of its heating field and to mount same on the rim of an assembly opening of a hob with a carrying rim provided on the hotplate circumference, much as with cast metal electric hotplates. Here again the hob zones adjacent to the heating field can be in one plane and can be connected approximately uninterruptedly to the hotplate.
This and further features of the preferred further developments of the invention can be gathered from the description and drawings and the individual features can be realized individually or in the form of subcombinations in any embodiment of the invention and in other fields.